The present invention is generally directed to detecting objects, and more specifically to discerning whether a detected object is in a vehicle path.
Increasingly, vehicle manufactures are installing safety devices in vehicles to enable drivers to drive in a safer, more efficient manner. For example, some manufactures have included forward looking systems (FLSs), rear detection systems (RDSs) and side detection systems (SDSs) within certain vehicle models. An adaptive cruise control (ACC) system is one example of a FLS.
A typical ACC system uses a sensor (e.g., a radar or laser sensor), mounted at the front of a host vehicle, to detect objects in the forward path of the vehicle. When an object is detected, the ACC system typically compares the projected path of the vehicle to the object location such that objects on the roadside or in different lanes are eliminated. That is, if the lane ahead is clear, the ACC system maintains a set vehicle speed. However, when a slower vehicle is detected that is in the vehicle path, the ACC system maintains a driver selected distance (using throttle control and limited braking) between the vehicles. A typical ACC system uses a mechanically scanned radar sensor, which normally improves the ability of the system to detect targets (e.g., other vehicles) in heavy traffic. A typical commercially available ACC system has a range of one-hundred fifty meters, an azimuth coverage of fifteen degrees and updates approximately ten times per second. ACC systems generally determine the range of a detected object, as well as the relative speed of the detected object.
However, commercially available FLSs have been known to provide false alarms (e.g., a visual or audible) or to apply throttle and brake control when the FLS detects an object that is not in the vehicle path (e.g., overhead bridges and overhead signs). One approach to eliminating false alarms or inappropriate brake and throttle control is to use a sensor (e.g., radar or laser) with a sufficiently narrow elevation beam such that the main beam does not illuminate overhead objects at the maximum warning range (e.g., one-hundred meters). For automotive applications, this approach has not proven particularly practical due to packaging constraints, which limit the dimensions of the antenna that can be utilized. Further, reducing the width of the elevation beam, to eliminate overhead objects, generally results in the need for multiple elevation beams or beam scanning to ensure that valid targets are still detected given the expected variations in vehicle orientation and road geometry. In addition, implementing multiple beams or beam scanning adds additional cost to a given FLS.
Another approach that has been utilized to distinguish overhead objects from valid in-path objects is to estimate target height by incorporating elevation measurement capability, such as elevation scanning or monopulse, within the sensor of the FLS. However, implementing such schemes also adds additional cost to a given FLS. Another technique for distinguishing overhead objects from valid in-path objects is to examine the lateral extent of the object. For example, bridges typically extend across a roadway, while the lateral extent of an individual vehicle is typically less than a lane width. However, multiple vehicles stopped at a substantially similar range may extend across multiple lanes and thus appear to the FLS as an invalid in-path object, e.g., a bridge. In addition, many overhead signs (e.g., an xe2x80x98Exit Onlyxe2x80x99 sign for a given lane) are approximately the width of a single lane of a roadway. These limitations tend to decrease the usefulness of examining the lateral extent of an object to determine whether the object is a valid in-path object.
What is needed is a practical technique that prevents a FLS from providing an alarm and/or implementing throttle and brake control when a detected object is not in a host vehicle path.
The present invention is directed to a technique for distinguishing an overhead roadway object that is not in a host vehicle path from a substantially motionless roadway object that is in the vehicle path. Initially, a plurality of sensor scan signals are provided into an anticipated path of a host vehicle. Next, a plurality of object return signals, that correspond to reflections of the plurality of sensor scan signals, from at least one detected stationary object are received. Then, an average amplitude slope of the return signals, as a function of the range to the at least one detected stationary object, are determined. A sufficiently positive amplitude slope identifies the detected stationary object as an overhead roadway object that is not in the vehicle path. A sufficiently negative amplitude slope identifies the detected stationary object as a substantially motionless roadway object that is in the vehicle path. In another embodiment, when the average amplitude slope is ambiguous, an average amplitude deviation in the return signal is determined as a function of the range to the detected stationary object. An average amplitude deviation that is above an amplitude deviation threshold indicates that the detected stationary object is an overhead roadway object that is not in the vehicle path. An average amplitude deviation that is below the amplitude deviation threshold indicates that the detected stationary object is a substantially motionless roadway object that is in the vehicle path.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.